Method of purifying gases



June 14, 1960 E. K. PLANT METHOD OF' PURIFYING GASES Filed Oct. 15, 1956 Evi INVENTOR. 'W//v K. Pza/vr Arroz/ver METHD (ISF PURFYING GASES Edwin K. Plant, Pittsburgh, Pa., assignor to ColumbialSouthern Chemical Corporation, Allegheny County, Pa., a corporation of Delaware Filed Get. 15, 1956, Ser. No. 616,102

8 Claims. (Cl. 18S- 119) The present invention relates to a method of purifying gases or vapors. In a particular embodiment the present invention involves the removal of iron chloride from a gaseous mixture thereof. When, for instance, a titaniferous iron ore is chlorinated at high temperatures in the presence of carbon, an eluent gas comprising titanium tetrachloride and iron chloride is given o from the reactor. When ilmenite, for example, is the ore being treated, a substantial quantity of ferricchloride is present in the eiiiuent gas. Numerous methods have been attempted to separate the ferric chloride .from the titanium tetrachloride, but in each of these methods severe coating of the surfaces of the apparatus used has occurred, thus seriously hindering the process and VVcausing excessive losses.

Forexample, Wherea gaseous mixture containing ferrie chloride and titanium tetrachloride is to be cooled and ,separated into its components, ferrie chloride, which separates out as a solid upon condensation, deposits on the apparatus surfaces and cakes them, thus disrupting the ,efficiency or Vthe apparatus Vand upsetting proper heat transfer. if, for instance, a bank of tubes having a cooling uid running ltherethrough :is used in heat exchange with the gaseous mixture, solidferric chloride deposits on ,the-tube surfaces and forms an insulatory coatingthereon which, after a short period of time, substantially negates their effect asa coolant.

Where gaseous mixtures of the type just mentioned are admixed with an inert coolinggas yto eifect condensation o-theferric chloride constituent, a gaseous eluent containing a substantial amount of inert gas results and complicates the procedure by requiring that cumbersome v and expensive apparatus be used to handle the extra. volume of gas.

According to the present invention the difliculties here- 'inabove mentioned are overcome. Hot efuent gases dex through the condenser, they arein close proximity with a Vgradually thinning lining.

For example, a VVertical condenser, according to the instant invention, receiving hot furnaceV gases in theupper -portion thereof, which gases then ow downwardly ffthrough the condenser, is lbest heavily lined in the top portion thereof, the lining Ybecoming gradually thinner toward bottom. Suchavsyste-m permits controlled radiation ,of 'lteafhwitsitlie ,Walls .0f theatrale Furthermore, the condenser, as will be seen hereinafter,

`is so constructed that suiilcient heat hom gaseous nite States Patent O "ice mixture radiates through its Walls to condense vaporous' ferrie chloride to its solid state. One of the `exceptional features of this condenser is that it permits gradual radiant cooling with a minimum of coating being formed on the interior surfaces of the condenser. This is a significant contribution to an art hitherto crippled `by such cakin'g and coating. v 'Y The partially-cooled gaseous mixture containing iron chloride solids then passes to a zfone of relatively large cross-sectional area, such as'a settling box, where ferrie chloride solids selectively settle out.V Conditions ofte'riiperature andvelocity are maintained Within the settling 'box such as to allow the ferrie"chloride'particulatesTto fall freely, as it were, to the bottom of the'boxmwithojit any substantial adhesion of the particulates to thenner Wall surfaces of the box'and without their being entra',v ed by `the gaseous titanium tetrachloride leaving the'box. The titanium tetrachloride eluent is thus rendered sub- Y stantially free from ferric chloride.

These results are best realized'by maintaining the temperature of the mixture and that of the inner surfaces of the settling box walls at approximately the same temperature. By this isothermal system, caking or ,coating of the inner surfaces v vith ferrie chloride ycondensate is substantially prevented. Thus, the mixture traveling throughthe settling zone maybe conveniently Amaintained at an average temperature of about 250 F.V and the Walls ofthe zone at approximately the same temperature. VIf, -for 17instance, the mixture enters the zone Aor box at about 300 F. and the gas emanating from the box Vis at .about 200 F., the average inner walltemperature should lthen Vbe maintained at about 250 F. Latent heat ywhich escapes from the gaseous mixture does vso by radiation .through the Walls of the zone. Obviously, too much heat radiation would cause condensation of titaniumftet'rachloride and, thus, upset the "desirable 4selectivity ofthe process. Also, too great a gas Velocity through 'the 5system 4would cause entrainment of .ferrie chloride by the rapidly exiting titanium Vtetrachloride gas.

Vzjiccordinglto a ,particular embodimentof the present invention, the lower portion of a'vertical condenser ofthe Vtype just Vdescribed empties directly into the topportion of one end of a settling box, the gases flowing through the box at a velocity and `temperature such that `the iron chloride solids .formed in the condenser fall freely tothe bottom of the A.settling box, Vfrom whence they'v are ifelmoved by Va suitable means,such as a screyv conveyor.

As the gaseous mixture travels through the yzone, v me cooling takes place, as defined above, by liberation ff latent heat; also, by controlling the velocity and reside e ,time of the gases inthe cooling system, iron chlor e solids having a specic minimiim'particle sizernaybc vby providing a quiescent settling'zone or gas `Spacefto permit efficient precipitation' of iron chloride` solids.l 'A turbulent zone would tend to interrupt `pt l1elireelfall of solids'and also disrupt the vtemperature equilibriurifefxisting between the gaseousmixture andthe,internalnsurfzaees vof the zone by causing severe coatingfon ,thesefsurfaces and preventing efficient liberation of latent heat;

Asstated hereinabovaitis animportantfeature of the present invention that a method of selectively'removing Viron chloride, or the like, from a .gaseous mixture thereof has been vdiscovered which `provides continuous lprecipitation of the condensate substantially without caking and coating of the apparatus. Timeand vprofit .loss lsa `V.realli .of hither@ puede@ methods 'attenante @..ifn

` is optional.V

chlorides from gaseous vapors containing them yhave been verysigniiicantly minimized.

In the drawing, Figure l is a diagrammatic side elevationof a preferred embodiment of the present invention.

VFigure 2 is a vertical section along line lI-v-II of the condenser and settling box. Figurel is a preferred embodiment showing a shaft Vlong vertical chamber having a `shell of metal, `such as i steel, nickel and the like, 'and having a lining of refracfurnace 1 in which, for instance, ilmenite ore in the form of ore-coke briquettes is chlorinated by passing gaseous chlorine upwardly through the furnace 1 f ind,thus,V

through a body of the briquettes contained therein. The

resulting chlorinated gases pass through outlet 2 leading ,into cooling unit 3,7which comprises a vertical chamber I f `having tapered (brick) lining 4 and a metalY shellf5 through which heat from the gases introduced therein ra- 'diartes` Y As stated hereinabove, hot gases from the fur- ,Y 4.naceenter the cooling chamber 3 atuthe point in Vthe chamber having the thickest lining. In the present case, Y Athe gases enter chamber 3 at the topthereof where the lining 4 isvrthe thickest. Y

'I'he process of the present invention is particularly Aefficacious when usingra theoretical excessief chlorine gas -to chlorinate the titaniumY ore, thus permitting Vfree C125 to be present in the chlorinated eluent gases. Furthervmore, the process of the present invention isY not restn'cted to the static, briquette bed operation just dened, `since it may be employed in uid bed chlorination processes,.moving bed processes, and the like. Y

" The lower portion of cooling unit 3, according tothe instant embodiment, opensinto collecting box or gravi-l tational settling box 6 having screw conveyor 7 on the bottom thereof and outlet 8 leading therefrom.r Screw Y conveyor -7 is driven Vby motor 9 and'feeds into outlet 10 which empties into storage tank `11. Outlet 8 is connectedto'sp'ray cooler 12, which, in turn, is directly Yat- -Fi'gure 2is a vertical section along line lI--II of Figure l. This gure discloses how the sides of collecting "the ilmenitel ore-,carbon briquettes above deiinedat an l velevated temperature, said gases comprising titanium tet-A Yrachloride and ferrie chloride, are introduced into cooler 3 from 'furnace `1 via outlet 2.1 These gases at a tem-- fperature between about 1600 Fgand 18009. F., usually Y toward the top of the Ycooler and then downwardly therethrough. In so doing, as will be seen hereinafter, 'theyradiate heat through the-walls thereof, thusV gradually Y Y:andeiiciently being cooledruntil ferric 'chloride solids are formed.

' The resulting gas-solid mixture enters collecting box 6 ata temperature of about 300 F. v As the mixture passes horizontally through` the box, ferricrchloride solids settle out Vand areY removed via conveyor 7 and outlet 10 to storage tank 11.

Y v Titanium tetrachloride gas having aV temperature between about 200 F. and 250 F. emanates from collect'- Y ferred by means of pump 14 to storage tank 15. Part'of the liquid condensate from tauk'13 is returned to the top Y Y of spray'cooler 12 (as shown), where it serves Yas the spray coolant described above, the condensate being first cooled in cooler 16. Y

Cooling chamber 3 referred to above is a relatively about 1750 F., as they enter the cooler 3, pass upwardly tory material, such as insulatory iirebrick. The lining is thickest in the top portion of the chamber and gradually diminishes in thickness toward 'the bottom, thusY permitting varying Vdegressiorr of heat -radiation V,through the walls of the chamber as the gaseous mixture passes therethrough. Y

The degree of radiation is so regulated as to permit gradual cooling of the gaseous mixture passing through the chamber without any significant,V coating ofthe inner surfaces of the chamber, such as is typicalofcold-wall Ycooling techniques hitherto known. Y j

YWhen the gaseous mixture. enteringrthe chamber comprisestitanium tetrachloride andfer'ric chloride a-t a temperature of about 17509 F., heat radiation Vshould be such as to permit a mixture comprising `TiCl4 gas and FeC13 solids to leave the chamberY at atemperature of 'about 250 Ejrqsso" F.7preferab1y--jabour"300 Ar Y Ylower temperatures, -TiClft'endsto condense to a liquidY state and form a sludge on the interior walls.

VFrom the cooling chamber 3,the gas-solid mixture passes directly'into collecting box 6, usually made of metal, such as steel, although any metal capable of Y,withstanding the rtemperature and corrosive conditions of Vthe present process is suitable. In passing through box s, the mixture sheds Feel, solids which fau freely to the bottom of the box and are'removed by any suitable means, such as a screw conveyor 7.

' Since, as disclosed hereinabove, the gas-solid mixtureY is best introduced into the settling or collecting box 6 ata temperature oftabout 300 F., in the case where a mixture comprising TiCl.,t gases and FeCla solids concerned, and the TiCl4 `gases removed from theY box are between about250 F. .and.200 F., the average temperature throughout the box is aboutV 250 F.Y It has been found, according tothe present invention,rthat by Vmaintaining' an isothermal Ysystem, i.`e., by maintaining the interior surfaces of the collecting unit as well as the gases therein at an average temperature of about 250 F., caking'or coating of the'interior surfaces ofthe unit is substantially eliminated aridan eicient Ysystem ,results. Y

Obviously, since ilexibilityfis at times needed. 'in a continuous system, it may be desirable to jacket the col-Y lecting unit to aiord Yready control of the temperature thereof and in thatY way maintain the isothermal system herein defined. Y A Ajacket placed about the unitV may be employed for that Vpurpose and temperature controlled by passing steam or water therethrough, for example, at a predetermined temperature. 'e Y What latent heat is lost from .the mixture-n transit throughfboxy 6radiates through the walls thereof and condensation of the gases on the interiorlsurfaces is thus very significantly reduced. ,Y

Eddy Ycurrents which tend to form in'thersettling box v6 may be ,adequatelyY minimized by hanging chains or the like in the path of the moving body o f gas, thus maintaining a relatively steady linear ow of gas throughthe Y box. 6o l Y' The following is an example of aV particularly desirable embodiment of the present invention:

Example I K Into brick-lined cooler 3, 48.8 moles of gas perrhour is fed from furnace 1, the gas being at a temperature of 17509 F. and having the following components inY ap proximately the proportions given:

Cooler 3 is fed via furnace outlet 2 which opens into the upper portion of the cooler, the gas passing first upwardly through the cooler and then traveling downwardly toward collecting box 6.

The cooler is cylindrical, measures 32 feet in height and is made up of three sections. The iirst section or upper third is twelve feet high, measures 9 feet in average diameter, has a one-foot thickness of brick (K=0.65), andan area of 340 square feet. The second section or middle third of the cooler 3 is ten feet high, measures 8.5 feet in average diameter, has a six-inch thickness of brick (K=0.65), and an area of 267 square feet. The third section or lower third is ten feet high, measures 8.2 feet in average diameter, has a 3.5-ir1ch thickness of brick (K=0.65), and an area of 257.7 square feet. The shell 5 of cooler 3 is made of one-half inch nickel clad steel. Since the coeiiicient of heat conductivity (K)` is the same for all three sections, and since the heat transmitting resistance of the wall is directly proportional to wall thickness, obviously the wall of the cooler diminishes in heat transmitting resistance from the top to the bottom of the cooler in the direction followed by the gases.V

At a relatively constant temperature vof 325 F. along the outside wall of cooler 3, the heat loss in section one of the cooler 3 is about 259,000 B.t.u., thus coolingthe gaseous mixture to l160 F. In section two, the heat loss is about 199,000 B.t.u. and the temperature of the gas as it leaves this section is 616 F. As the gas passes through section three, a quantity of heat equivalent to 115,000 B.t.u. is given up and the gas temperature reduced to 300 F. At this temperature the gaseous mixture comprises gaseous TiCl., and FeCl3 solids.

In a settling box 6 of the type depicted in Figure l, the box being feet wide, 30 feet long and l0 feet high and having a triangular cross-sectional area of 75 square feet, this mixture of TiCl4 gas and FeCl3 solids is introduced. The box is made of l0 gauge steel and is covered on all sides -with magnesia block insulation (K=0.04) having a 4-inch thickness. At the bottom of the box is a screw conveyor running the length thereof. The diameter of the screw is l2 inches and it is motor-driven at the rate of about l5 revolutions per minute.

The gaseous mixture ows through the box at a rate of about 6.33 cubic feet per second; hence, the average Velocity of the gas in the box is about 0.0844 feet per second. The temperature of the gas entering and leaving the box is about 300 F. and 200 F., respectively. Operating at the average inside wall temperature stated above (about 250 F.) and simultaneously at an outside wall temperature of about 60 F., the heat loss is Vabout 22.8 B.t.u. per hour per square foot, computed as follows:

1==20-9=22.s emma/sq. fr.

The total surface area of the box is:

Square feet Total surface area 1350 Hence, the total heat loss is 22.8 x 1350 or 30,700 B.t.u. per hour. At this rate of loss the 43.0 moles of gas (i.e., 48.8 moles fed into the box minus the 4.9 moles of FeCl3 removed therefrom) leaving the box is at a temperature of about 200 C.

Since a certain amount of the solids may adhere to the inner Walls of cooler 3, it is within the contemplation of the present invention (as stated hereinabove) to provide a control exterior to and adjacent the box, such as a jacket. 'Ihis provides ilexibility to the process, since the jacket may be used for heating or cooling, as the case requires.

' PeCL, solids'formed as shown above settle to' tlzlegbot tom of the box, the smallest solid particles being about 10 microns in diameter. T iCl gas containing a very small amount of FeCl3 solids is removed from the box and conducted toY a spray cooler where it is Vcondensed to liquid TiCl., by the process previously deiined.

rI'he diameter` of the smallest particle is determined as follows:

The rate of fall of a spherical particle, such as FeCl, in still air is computed from the following formula:

u-TT

The density of `FeCl3 is 2.8.

If l is the actual settling rate in feet per second of the smallest particle to be collected, Q the gas iiovv in cubic feet per second, Ac the cross-sectional area in square feet, and L and H the length and height in feet,

respectively, of the settling chamber, then obviously the Eddy currents which tend to aiect the particle size just computed can be minimized by hanging chains, or

D2 100.5 microns D the like, in the settling box.

The cross sectional area of the settling box should not be of such magnitude as to upset the isothermal system hereinabove defined. For instance, too sharp a -reduction of the gas velocity brought about by a large cross sectional area could increase the residence time of the body of gas in the settling box to such a degree that the isothermal system herein dened would be impossible of maintenance.

It is evident from the foregoing that numerous modifications within the skill of a chemical engineer may be applied to the present process without transcending the scope of the invention. It is also evident that gaseous mixtures containing other than iron chloride solids may be treated as herein dened. For example, a zirconium tetrachlorideontaining mixture may be liberated of its ZrCl4 content by the process of the instant invention, the ZrCl., having been produced from a zirconium-bearing ore in a system such as that shown herein. Zirconium tetrachloride condenses from a vapor to a solid in the same manner as ferrie chloride. The temperature of the gases entering the cooling system of the present invention and containing ZrCl4'would vary, depending upon the type zirconium-bearing material being treated. For instance, zirconium carbide or zirconium carbonitride can be chlorinated at temperatures between about 650 F. and 750 F. and zirconium oxide between about 750 F. and 1650 F.

While the instant invention has been described with particularity as to certain embodiments thereof, it is not intended that the scope of the invention be so limited, except insofar as particularly dened in the appended claims.

I claim:

l. A method which comprises cooling a Agaseous mixture containing iron chloride vapors by passing the mixture through an elongated zone having walls capable of transmitting heat, which walls diminish in heat transmitting resistance in the direction followed by the mixture through said zone, gradually cooling said mixture in said zone to the point where the iron chloride is in solid state and a gas-solids mixture results, introducing said gassolids into arelatvely large, quiescentgas'space having passing saidmxture throughtlleispasY at @ratejof flow/ivV at whichfsubstantially all ofthe ,solid iron chloride component selectively settles out,

y ing the temperature of the gaseous mixture, the gas space vand the innerfsurfaces of the Ywallsopposite said ilowing 2.*The process of claim 1 wherein suicient residence time of said gas-solids mixture in said space isprovided t to permit iron chloride solids having a particle size of at least l0 microns to settle out. f Y B-Thevprocess of claim l wherein the f 4; The `process of llaim 3 wherein ufficientfresidence 1 time of saidg'as-solidsrmixture in said space is provided toperniitferic Ychloride solids having aparticlesize of atleast 10microns,Y to Settle out.

5.v AV method which comprises coolingfa gaseous mix- Y ture containing iron chloridevapors by passing the mixturethrou-gh an elongatedv zone having 'wallsy capable of transmitting heat, which .wallsdiminish in heat `transmitting resistance'in a ldirection"followed by vthe mixture Y Y iron, chloride Y selectively removed from a gaseous mixture of titaniumv Y Vte'trahloride 'vapors' and iron chloride vapors.` Y Y through said zone, -graduallycooling said mixture in said zone .to the point where'` theiron chloridaislsolid, state and a gas-solids mixture results, andseparatingfthe. solid iron chloride from the mixture. t ,I

6. The method of claim 5 wherein .the gaseous mix'- ture enters an upper portion of said zone and VHows downfA wardly therethrough to a lower portion thereof, the gasf, solids mixture formed is a gaseous suspension Yof solid iron chloride particles, and the walls of the zone "diminish` in thickness from Vsaid upper portion to said lower portion.' 7. The method of claim V6 wherein the gaseous mix# ture is gradually cooled as itflows downwardly through said'zne bytransmission oftheat from the gaseous mixture through said walls. e

l8.` Thermethod of claim jjwherein theV gaseous" ture comprises iron Vchloride Vand titanium tetrachloride Y Muskat et al. L June 10, 1941 A2,245,358 Pechukas June Y'10, 1941 2,311,466`V Pechukas Feb. r'16, 1943 2,420,373 Hogberg 'May 13, 1947 v2,675,890 Frey et al; j Apr.V 20,1954

or UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. V.2,940,541 June 14, 1960 .Edwin K., Plant It is hereby certified that error ap pears in the above numbered patent requiring correction and that the sai d Letters Patent should read as corrected below.

Column 5, line 33, for "In" read Into n; column line 21, :for "LA u2HQ" read M LAcurHQ line 23, for "valve" read Val'ue Signed and sealed this 25th day of April 1961.,

(SEAL) Attest:-

ERNEST W1, SWIDER DAVID L., LADD Attesting Officer Commissioner of Patents 

